The neuropeptide profile is being examined in animals treated with various neurotoxicants. Single injection of acrylamide (100 mg/kg; p.o. killed 24 hr after) failed to alter the brain (Met5)-enkephalin, substance P, or neurotensin levels. However, 10 daily injections of acrylamide (20 mg/kg/day) caused a selective increase in substance P content in striatum. This result suggests that substance P may be related to the tremor seen in acrylamide-treated rats. Repeptive administration of kepone (10 mg/kg/day; p.o. for 10 days) caused a 40% decrease in pituitary (Met5)-enkephalin in male rats. Since there is a sex difference in pituitary (Met5)-enkephalin content (female's content is about 60% of males), plus the reported estrogen-like action of kepone, these results tend to suggest that pituitary enkephalin may be under the regulation by gonadosteroid hormones.